1. Field of the Invention
The present invention relates to an ink jet head, a method for manufacturing such a head, and a recording apparatus provided with such a head. Particularly, the invention relates to an ink Jet head wherein at least a part of its head is sealed with resin, a method for manufacturing such an ink jet head, and ink jet recording apparatus using such a head.
2. Related Background Art
An ink jet recording method in which a recording is performed by generating ink droplets and causing them to adhere to a recording medium such as paper, plastic, and cloth is a recording method which makes extremely limited noises at the time of recording, is capable of performing a high-speed recording, and using an ordinary paper sheet. Among such methods, the so-called thermal jet recording method which utilizes an exothermic element for generating energy thereby to discharge ink for recording attracts a particular attention in recent years.
As a method for manufacturing the thermal jet recording head, there is known a method to fabricate the discharging element which constitutes the principal part of the so-called thermal jet recording head in such a manner that heat generating or exothermic elements and wirings for the exothermic elements are formed on a silicone substrate by the application of the thin film technology, for example; the grooved walls for ink passage and the wall for a common ink chamber are formed by a photo-lithography process using a photosensitive resin; a flat cover made of glass or the like is coupled to the walls; the discharging element having a filter bonded to the inlet of the common ink chamber is fixed to a base plate together with a PCB; the electrical connection between the discharging element and the PCB is made by a wire bonding or other methods; lastly, a front cover and an ink inlet member are fixed, and then, a sealing agent such as a silicone resin is filled in for the purpose of assuring its liquid tightness and air tightness. FIG. 1 to FIG. 3 are views illustrating the structure of the above-mentioned thermal jet recording head, respectively.
FIG. 1 illustrates the structure of the discharging elements. On a silicone substrate 101, an exothermic element 103 and a wiring 102 for the exothermic element are formed by the application of the thin film technology.. Further, the grooved walls for ink passage and the wall 104 for a common ink chamber are formed by a resin such as a photosensitive resin. On the upper end of the walls, a glass plate having a common ink inlet 107 is bonded. The common ink inlet provided for the glass plate 105 is covered by a filter 106 which is bonded to the glass plate 105.
FIG. 2 is a schematic view showing the structure of a thermal jet recording head. A discharging element 201 and a PCB (printed circuit board) 202 are adhesively fixed to a base plate 203 which serves as a supporting member to support the discharge element. Both of them are electrically connected by a wire bonding 206. To this, a front cover 204 having an ink inlet member 205 and a discharging window 207 mounted thereon is coupled, and as shown in FIG. 3, a silicone resin 301 is filled in for the purpose of assuring its liquid tightness and air tightness to complete a thermal jet recording head.
As described above, in order to fill in the gaps resulting from the adhesion of the discharging element and base plate, and the front cover and base plate, a silicone RTV (a type of silicone which is hardened at room temperature) is employed as an adhesive and sealing agent. The reason why it is employed is that this type of silicone has the following advantage:
(1) the silicone RTV is hardened in a rubber like state thereby to protect the discharging element from damages caused by a thermal shock and the like;
(2) hardening begins rapidly at the surface and there is no possibility that the filter and nozzles are clogged due to liquid drips, inverted flow, or the like; and
(3) being monoliquid, and hardening being completed in several hours at normal temperature and moisture, this silicone has an excellent operativity among others.
Nevertheless, there are encountered among the thermal jet recording heads fabricated as in the example mentioned above, the defective products having a problem of unstable discharging performance. This has been the task to be solved. Along with the increasing demand on an image formation which requires more preciseness, particularly on the formation of the highly precise color image recently, this task is the subject to which more attention is being given.
As a result of the detailed examinations to find the causes of the unstable discharging performance and other defects, the present inventor has found the following fact:
One of the components of the silicone RTV used as a sealing agent and adhesive agent, low molecular siloxane is caused to diverge in an extremely fine quantity in a process of being hardened or after hardened and adhere to the surface of the exothermic element and others. Particularly, when it is caused to adhere to the surface of the exothermic element in a film like state, the generation of "air bubbles" required to discharge liquid becomes insufficient, resulting in the irregularity of the speed at which to discharge ink droplets, the irregularity of the volume thereof, or the like, so that the normal ink discharging is hindered. Consequently, the degradation of dot positional precision (the so-called biased dots), defective dot sizes, and the like occur, and it is found that these are causes for the hindrance to stabilizing the recording. Also, the biased ink discharging is particularly caused by the fact that the low molecular siloxane adhering to the surface where the discharge ports are arranged affects the wettability of the surface. Thus, when a thermal jet is used, the adhesion of the low molecular siloxane directly produces an adverse effect on the performance of the ink discharging. Also, the silicone RTV currently available on the market or being used in general always diverges the low molecular siloxane in the process of being hardened or after hardened. There is no exception. Therefore, the elimination of the disadvantages brought about by the low molecular siloxane in using the silicone RTV has been a major problem to be solved.